This invention relates generally to the tinting or coloration of contact lenses for human eyes.
For some time now, it has been possible to correct or improve the vision of the human eye by disposing a small, transparent lens directly upon the surface of the eyeball. The contours of this contact lens supplement and correct the effects of the biological lens within the eyeball.
Early contact lenses were primarily of the "hard" variety. More recently, however, so-called "soft" contact lenses have been introduced, and these lenses have met with considerable popularity. "Soft" contact lenses are manufactured from a hydrophyllic plastic material; that is, they can absorb and retain water, and become soft and pliable upon the absorbtion of water. They are relatively comfortable for the user to wear, and can be worn for relatively long periods of time.
Tinted or colored "soft" contact lenses have advantages or attractions to a variety of contact lens users. Tinted lenses provide cosmetic improvement for persons having one, or both, eyes which have been disfigured by illness or accident. Tinted lenses can be used by patients with diplopia to make them appear more normal. Also tinted lenses may provide albino and aniridic patients with improved general facial appearances. Suitably tinted lenses can also reduce light transmission and give the patient increased visual comfort.
Several methods of coloring central areas of contact lenses are suggested in U.S. Pat. No. 4,252,421 to Foley, Jr. However, the tinting or coloration of contact lenses is not a simple task. If colors are printed on transparent lenses, the coloration may not be uniformly dispersed through the lens material. Moreover, the color printed upon such lenses tends to fade after several cleanings or autoclavings.
It is important that the tinted or colored lens provide a natural appearance in the wearer's eye, of course. Thus, a natural-appearing soft contact lens should have a clear central area, a colored intermediate area and a clear outer area so that the colored portion will not cover the sclera of the eye. Moreover, the central portion of the lens should be uncolored to permit maximum light passage into the eye interior. Thus, it is desirable to be able to provide the lens with a ring-like annular tinted area, surrounded by clear, untinted lens material.
In manufacturing single-part tinted lenses, several problems can arise in mounting a lens on a tinting fixture. It is important that the worker not handle the lens directly with his or her fingers or fingertips, because the minute amounts of oil contained on the worker's fingertips will prevent the dye from being accepted or absorbed evenly by the lens. If the worker uses gloves, dexterity can be reduced. This dexterity is important in manipulating the small lenses and centering the lens on the tinting fixture. If the worker uses tweezers and manually mounts the lens on a fixture, lens production can be slow, and accuracy in the mounting may be compromised.
As suggested above, it is important that the tinted annular area of the lens, and correspondingly the clear central portion be precisely defined and accurately located. That is, even slight fuzziness or running of dye colors into otherwise uncolored areas of the lens will be immediately apparent. Fuzziness or tint runs will necessitate the rejection of the finished lens product.